This invention relates to catheters which are used to provide access into the human body. More particularly, the present invention is directed to steerable sheath catheters which are used to provide access into the human vasculature for delivery of additional tools, instruments, medications or fluids.
Catheters have been commonly used in medical practice to reach locations inside the body otherwise unreachable without surgery. The body of a catheter is long and tubular and contains an inner lumen. A catheter has a distal end or tip which enters the patient as well as a proximal end that has a handle for control by the operator.
The tip of the catheter is first inserted into a major vein, artery or other body cavity. The catheter is then further inserted and guided to the area of concern. The catheter is often used as a delivery method for other tools, such as balloons for performing angioplasty or a camera for performing endoscopy. As medical knowledge increases, the catheterization procedures have become more complicated and more exacting. The usefulness of catheters is largely limited by the ability to successfully manipulate the position and orientation of the catheter tip into small and tortuous vessels. Therefore the goals for a successful catheter design are to maximize the inner diameter while minimizing the outer diameter and maintaining control and flexibility of the catheter body. The catheter operator should be able to easily steer and maintain the catheter shape during use. Additionally, the operator should be able to easily deliver additional tools, instruments, medications or fluids through the inner lumen or lumens by having direct, unhindered access to the inner lumens at the distal end of the catheter.
One method of directing a catheter into position is through the use of a guide wire. First the guide wire is fed into position within the patient. Then the catheter is urged over the guide wire. However, it is not uncommon for the position of the catheter tip to become dislodged from the desired location as the guide wire is removed.
To avoid this problem, other catheters known in the art, are guided into place without the use of guide wires. These catheters have sufficient pushability that the tip of the catheter can be directed from a proximal location without buckling or kinking. Unfortunately, such guide catheters tend to be more difficult to steer into position and the necessary stiffness can limit their placement in areas with sharp curves.
Catheters with tips preformed into particular shapes specialized for specific applications are known in the art. The pre-shaping of the catheter may aid the placement of the tip in the desired location. However, the pre-shaping of catheters for particular applications requires a hospital to provide a wide array of catheter shapes and sizes for use. Another disadvantage to preformed catheters is that they do not allow the physician to adapt the catheter to account for any peculiarities of a patient's vascular system. A physician can attempt to reshape a catheter before use, by applying heat. However, such manual reshaping is not only time consuming but can compromise the lumen of the catheter, by causing the circular lumen to ovalize or flatten out as the catheter is bent, or even kink or seal at a bend destroying the catheter's usefulness.
Steerable sheath catheters, the present invention being one example, are also directed into position from a proximal location. However, the tips of these catheters are steerable due to the action of one or more pull wires that are embedded along the length of the catheter body. Pre-forming of the catheter is not necessary because the operator can adjust the shape of the catheter or steer the tip as the catheter is directed into the body. Therefore these catheters are capable of use in a wider range of procedures than the specialized preformed catheters.
A current method in the art used to manufacture steerable sheath catheters is to form the catheter on a mandrel using multiple layers: an inner liner, a layer of wire braid and an outer thermoplastic jacket. The inner liner is pulled over the mandrel and tightened down. The pull wire is laid axially along the inner liner, often within a groove present on the surface of the mandrel. The steel braid is pulled or woven over the inner liner and pull wire. After the steel braid is tightened down, the entire catheter is encased in a thermoplastic outer jacket. The outer jacket is then encased in heat shrink material and heated. The heat causes the thermoplastic jacket layer to flow, which when teamed with the pressure from the heat shrink material causes the thermoplastic outer jacket to flow into the steel braid consolidating the catheter into one unit. Examples include U.S. Pat. No. 5,669,920; U.S. Pat. No. 6,042,578; U.S. Pat. No. 5,527,325.
The mandrel in this process usually has a longitudinal groove to facilitate the placement of the pull wire during the manufacturing process. The inner liner of the catheter is placed over the mandrel and is pushed into the groove. The pull wire is then laid in the groove on top of the inner liner. The steel braid and outer jacket can then be pulled easily over the mandrel without disturbing the pull wire. However, the use of this process results in the creation of a bulge in the central lumen. This reduces the useable diameter of the central lumen for the insertion of other instruments. In general, it is desirable to maximize the ratio of the inside diameter to the outer diameter of the tubular body of the catheter.
Another problem in the current art is that by embedding the pull wire through the action of a thermoplastic polymer teamed with a heat shrink material or embedding the wire in the catheter body by spraying the outer jacket material over the wire is that the pull wire creates its own lumen, for example as shown in U.S. Pat. No. 6,030,371. Therefore the pull wire and its lumen are approximately equal in diameter. This creates three related difficulties. First, there is friction created between the walls of the lumen and the pull wire as an operator attempts to control the catheter by moving the pull wire. The friction increases the difficulty in operating the pull wire. Second, as the catheter is deflected (bent) through the movement of the pull wire, the steel braid embedded in the outer wall of the catheter is also pulled and flexed. As the steel braid flexes, the forces created can deform the lumen. This can cause the steel braid to lock down on the pull wire and the pull wire lumen. This greatly increases the friction and can prevent movement of the pull wire as the pull wire lumen is deformed from a circular shape into an ovular shape. The third problem is that as the pull wire is “locked down” in the bent catheter, the pull wire and catheter lose the ability to spring back to the original shape as the force on the pull wire from the operator at the proximal end is removed. Accordingly, there remains a need in the art for a catheter with a pull wire with reduced friction and reduced interference from the steel braid which would allow for easier control by the operator and would allow the catheter to return to its original shape.
The pull wire of a steerable catheter is generally manipulated by use of a control handle including a steering mechanism. Control handles and steering mechanisms are available in many different designs according to the number of pull wires, type of catheter steering mechanism used, access ports and desired end use for the catheter. It is preferable that any steering mechanism should be able to be actuated without requiring substantial hand movement and the handle should provide for near simultaneous actuation of both proximal and distal steering. The handle must also be able to meet all appropriate environmental and sterility requirements likely to be encountered. The handle should be able to hold the catheter tip in a bent or deflected condition until the operator actively changes deflection.
In the construction of steerable guide catheters it is additionally beneficial, as previously discussed, to maximize the diameter of the central lumen. Additionally, it is imperative that additional tools and instruments can readily be inserted into the lumen without snagging or jamming in the lumen. In the prior art, the lumens are often not continuous and frequently have a permanent bend as the lumen transitions from the area within the proximal handle portion to the lumen in the catheter body. The discontinuity and indirect route are disadvantages of the current catheter handle and control mechanism designs.
There are two reasons why the catheter body is not continuous until exiting the handle: first, the pull wire must be accessible in order to be attached to the control mechanism within the handle. When the catheter body is manufactured, excess pull wire is left exposed at the proximal end or the body portion is trimmed away to expose sufficient pull wire. However, for convenience of the user the control mechanism usually appears in the middle of the handle where it can easily be manipulated by the user's fingers or thumb, not the end of the handle where the end of the catheter body should be to allow access to the lumen. The prior art solution to the problem of needing access to the pull wire within the handle, is to form a joint in the tubing, including the lumens. The end of the catheter body is placed near the connection point for the steering mechanism. For example, see Gould et al., U.S. Pat. No. 4,586,923. A connecting tube is then glued to the catheter body to extend the lumen towards the exit at the proximal end of the handle, while leaving the pull wire free to attach to the control mechanism within the handle. As it is important for the joint to be strong and not leak, one method of joining is to secure the catheter body inside the connecting tube. This style of attachment causes a size change between the tube end exposed to the user at the proximal end of the handle and the actual size of the lumen inside. This may cause the user to insert the wrong size tool which then jams inside the handle. The user may waste several sterile tools before the one that fits is found. As all these products are sterile and cannot be reused, the search for the correct fit is a waste that could be avoided.
Additionally, the joint, of either an overlapping type described above, or a butted joint, may impede the insertion of instruments. In the overlapped joint, the instruments are likely to hit or be snagged upon the catheter body inside of the connecting tube at the position of the joint. At best, the operator will have to redirect the inserted instrument passed the blockage into the inner lumen, and at worse may damage the instrument being inserted. In a butted joint where the two tubes are glued end-to-end, there is a potential problem if the joint is not made exactly, or if glue leaks inside of the joint that may cause blockage similar to that with the overlapping joint. Also, if the lumen is to be used for the delivery of fluids or medication, there is the potential at any joint for leakage, which may be detrimental by contaminating any samples that are being taken, delivering an imprecise amount of medication, and fluid escaping the lumen and entering the handle body and leaking out into the sterile surgical environment.
The second problem preventing the use of a continuous, direct catheter body is the type of control mechanism used. Often the bulk or design of the control mechanism limits the size of the lumen, or lumens as shown in U.S. Pat. No. 5,571,086. The design may also force the redirection of the lumen, or lumens to avoid parts of the control mechanism. Both are disadvantages when use of the lumen is desired for the insertion of tools.
There is a need in the art for a simple steering mechanism. One that is simple to use, easy to construct and low in cost. There is also need for a steering mechanism that does not impede the central lumen by requiring additional joints, bends, or variation in size of the lumen.
It is preferable that any steering mechanism should operate without requiring substantial hand movement and the handle should provide for near simultaneous actuation of both proximal and distal steering. The handle must also be able to meet all appropriate environmental and sterility requirements likely to be encountered. The handle should be able to hold the tip assembly in a bent or deflected condition until the operator actively changes deflection.